Time-resolved spatial profiles of electron density and temperature in hydrogen plasmas induced by radiation from laser-produced tin plasmas for extreme ultraviolet lithography light sources

Abstract

We observed the spatial and temporal changes of the electron density (n e) and the electron temperature (T e) of hydrogen plasmas around a laser-produced Sn plasma EUV source. The plasma parameters were measured by the laser Thomson scattering (LTS) method. In the experiment, the Sn plasmas are produced in H2 gas at a pressure of 50–200 Pa and the hydrogen plasmas were induced by radiation from the Sn plasmas. The LTS measurements were performed at distances 30–90 mm away from the Sn plasmas. In all cases, the strong bremsstrahlung radiation of the Sn plasmas easily overwhelmed the weak LTS signals. To suppress noise due to the radiation, the solid angle of radiation from the Sn plasmas was restricted. The experimental results show that the n e was in the order of 1017 m−3 and T e was around 0.7 eV.